A typical surround sound home audio system uses multiple speakers driven with separate audio channels to create a “surround sound” listening experience. The most prevalent system currently is a 5.1 channel surround system that requires five speakers for left, center, right, surround left, and surround right channels, as well as a subwoofer for low frequency environmental effects (LFE). With proper placement of the speakers in front and in back of the listener (i.e., to the listener's front left, front center, front right, rear left and rear right), these systems create the sensation of being surrounded by the sound of a movie, music performance or other desired audio environment. However, the multiple speakers used by these systems make them over complicated for most home users to set up and configure properly. In particular, it is difficult and expensive to unobtrusively position and wire speakers in front and behind the listening position (chairs or couch) of a home theatre. These systems are further complicated by a need to conduct setup testing to adjust the speaker placement and amplifier balance to achieve the best surround sound listening experience.
Virtual surround systems use sound localization techniques to produce the sensation of a full surround sound field using a simple stereo pair of speakers. These sound localization techniques map the surround sound channels (e.g., the 5.1 surround channels) into a virtual space, creating the perception of sound sources (the missing speakers) to the sides and behind the listener without actual physical speakers positioned there. One approach to virtually localizing sound sources uses filtering with a head related transfer function (HRTF). An HRTF models the frequency response of the human head and ear as a function of the source direction. When the HRTF-based approach is used with speakers, it typically requires careful crosstalk cancellation to achieve good localization precision. Virtual surround systems therefore have used interaural path cancellation (also called interaural crosstalk cancellation) together with the HRTF processing. The interaural path cancellation attempts to isolate sounds intended for the left ear to the left speaker, and sound to the right ear from the right speaker. A drawback to this HRTF-based approach with interaural path cancellation, however, is that it generally produces a very narrow “sweet spot” where the virtualization effect can properly be heard. In other words, the virtual surround sound effect can be destroyed if the listener turns his or her head, or moves slightly away from the sweet spot. The listener thus is required to sit in a very specific position in the room, and maintain a head position directly toward the center of the two loudspeakers.